Distance-Based Sensors Measure Up

When you visit someoneís house, you probably use the doorbell at the front door to let him or her know of your arrival. But a single doorbell in the lobby of a 20-story apartment complex doesnít make sense. Because there are many tenants, you must first determine the apartment you want to visit and alert just the people in that apartment (by buzzer, phone, or doorbell) of your presence.

Presence is helpful information in some cases, as in the first scenario. In that case, you push a button and someone knows youíre present. But sometimes knowing presence alone isnít enough, and you must also know location information, as in the second scenario. In that case, the location of the apartment you want to visit and a signal of your presence are both required.

Single-Pixel Technology, alternately known as background suppression (BGS), is ideal for ignoring objects in the background and for consistent detection of objects in the near field, regardless of their color or reflectivity.

Similarly in the world of sensing, presence is sufficient information for many industrial or commercial applications. And photoelectric presence sensing isnít just a staple of automation; itís a ubiquitous part of our daily lives. When our movement though an automatic sliding door is monitored to prevent the door from closing on us and when an intelligent faucet detects our hands and starts the flow of water, a photoelectric presence sensor is likely behind the scene. Photoelectric sensors serve their purpose of presence detection well. But simply detecting if something is present isnít always enough. Knowing that an object is within a certain range or identifying an objectís precise location may yield more helpful information. Over time, distance-based photoelectric sensing has evolved as the go-to technology when presence sensing doesnít cut it.

Today, three technologies have risen as the strongest methods of distance-based photoelectric sensing. They are Single-Pixel Technology (SPT), Multi-Pixel Technology (MPT), and Pulse Ranging Technology (PRT.)

Single-Pixel Technology, alternately known as background suppression (BGS), is the simplest principle to implement and the most frequently used. It utilizes the geometry of optics to determine whether an object is closer than a defined distance. For example, if cookies on a conveyor belt must be counted without detecting the belt or if the level of molded plastic parts in a hopper must be monitored without sensing the hopper surface, then SPT is the best sensing solution. SPT sensors emit a beam of light, typically infrared or visible red, which is reflected by an object back to the sensorís receiver.

The angle of that reflected light beam relative to the emitted light beam axis varies based on the distance to the sensed object. The closer an object is to the sensor, the larger the reflected light angle. The farther away an object is, the smaller the reflected light angle. So when the reflected light shines on one segment of the single pixel, the sensor recognizes that the detected object is in the near field. But when the reflected light shines on the other segment of the pixel, it is recognized as being in the far field and is ignored. SPT is ideal for ignoring objects in the background and for consistent detection of objects in the near field, regardless of their color or reflectivity.

The older alternative to this technology is diffuse mode sensing in which objects are detected based on the amount of reflected light energy. But diffuse mode sensing is prone to detecting background objects and has starkly different sensing distances depending on the objectís attributes.

Smart sensors is a promising area for innovation in 2013. The combination of more powerful processors, networking connectivity and mass customization of sensor designs is opening up lots of possibilities for more intelligent sensor solutions. Add to that wireless technology, especially for factory applications, and we can expect to see an area ready to keep developing new products.

Great article! We at XYZ Interactive Tech. have developed a distance-based IR sensor that merges the technique of angle measurement and signal strength of a reflected IR pulse. This can be done in a low-cost package to output distance with customized resolution and accuracy. We have extended this principle to design sensors in 2D and 3D to recognize hand gestures for "smart" switching technology applications.

Industrial workplaces are governed by OSHA rules, but this isnít to say that rules are always followed. While injuries happen on production floors for a variety of reasons, of the top 10 OSHA rules that are most often ignored in industrial settings, two directly involve machine design: lockout/tagout procedures (LO/TO) and machine guarding.

Load dump occurs when a discharged battery is disconnected while the alternator is generating current and other loads remain on the alternator circuit. If left alone, the electrical spikes and transients will be transmitted along the power line, leading to malfunctions in individual electronics/sensors or permanent damage to the vehicleís electronic system. Bottom line: An uncontrolled load dump threatens the overall safety and reliability of the vehicle.

While many larger companies are still reluctant to rely on wireless networks to transmit important information in industrial settings, there is an increasing acceptance rate of the newer, more robust wireless options that are now available.

To those who have not stepped into additive manufacturing, get involved as soon as possible. This is for the benefit of your company. When the new innovations come out, you want to be ready to take advantage of them immediately, and that takes knowledge.

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